The present invention relates generally to baseball and softball bats. In particular, the present invention relates to an insert for a ball bat, which is formed at least in part from at least one layer of composite material having an improved seam orientation.
Recent years have seen an emergence of new and improved tubular metallic softball and baseball bats. The most common tubular bat is the aluminum single-wall tubular bat. Such bats have the advantage of a generally good impact response, meaning that the bat effectively transfers power to a batted ball. This effective power transfer results in ball players achieving good xe2x80x9csluggingxe2x80x9d distances with batted balls. An additional advantage of such aluminum bats is the improved durability over crack-prone wooden bats.
Despite the advantages of tubular aluminum bats, there is an ongoing effort to improve the performance and durability of the conventional design. Generally speaking, bat performance is a function of the weight of the bat, the size of the hitting area or xe2x80x9csweet spotxe2x80x9d of the bat, and the impact response of the bat. The durability of a bat relates, at least in part, to its ability to resist denting and depends on the strength and stiffness of the tubular frame. While recent innovations in bat technology have increased performance and durability, most new bat designs typically improve performance or durability at the expense of the other because of competing design factors. For example, an attempt to increase the durability of the bat often produces an adverse effect on the bat""s performance.
More specifically, the impact response of a bat depends on the bat wall""s elasticity, rebound recovery time, and rebounding force. Generally, impact response is optimized when the bat undergoes maximum elastic deflection and then rebounds with the greatest force in the shortest amount of time. The elasticity of a bat can be increased by reducing the thickness of the bat""s tubular frame. In contrast, the durability of a bat generally is improved by increasing the thickness of the tubular frame. Consequently, a bat having a relatively thin tubular wall is capable of large elastic deflection, but may be vulnerable to undesirable local plastic deformation (or xe2x80x9cdentingxe2x80x9d). On the other hand, a relatively thick tubular wall is more durable but may be too stiff to achieve optimum slugging performance. Thus, enhancing one design aspect of a bat often compromises another.
Another example of competing design factors concerns the bat""s optimum hitting area or xe2x80x9csweet spot.xe2x80x9d The sweet spot is typically located near the center of the impact area of the bat. The performance of the bat drops off considerably when a ball impacts the bat outside the sweet spot, for example, near the end of the bat. When this occurs, the batter feels greater vibrations and transfers less energy from the bat to the ball. An obvious way to increase the sweet spot of a bat is to increase the length and circumference of the bat. This option is constrained by institutional rules and regulations. In addition, an increase in the overall size of the bat undesirably adds weight, often causing reduced bat speed and less slugging distance. (A hitter often can increase bat speed by using a lighter bat, thereby increasing the force transferred to the ball upon impact.
An example of a bat incorporating a composite insert is shown in U.S. Pat. No. 5,364,095. This patent discloses a tubular aluminum bat having a carbon composite insert to increase the xe2x80x9cstiffnessxe2x80x9d of the metal tube. The insert is made of multiple fiber layers, each layer having bi-directional woven fibers directed at 0 and 90 degrees relative to the axis of the bat. The insert is bonded to the barrel portion of the surrounding metal tube or frame and presses outwardly on the frame to produce a pre-load stress of several thousand pounds per square inch. The insert appears to be formed from multiple layers of glass and carbon fiber material (thickness of 0.03 to 0.05 inch) so as to be a self-supporting structure capable of withstanding several thousand pounds of compressive stress. This design gives the bat a relatively stiff, rigid tubular frame which appears to be capable of limited elastic deformation, a less than ideal trait if the goal is to optimize slugging performance. (One would expect this design to behave like a single-wall bat in which the compressive stress must be overcome before the wall begins to deflect.)
While composite materials offer the advantage of a high strength to weight ratio, such materials also present design challenges. Composite inserts and bat frames are prone to wear and tear due to the inter-laminar shear which can occur between bonded layers of composite material. The deflection caused when a ball impacts the bat produces shearing stresses between the composite layers, sometimes causing the bond between adjacent layers to fracture or separate (especially over time).
Additionally, the composite materials are typically formed as sheets, which are wrapped into a generally cylindrical shape. These sheets typically have seams formed where two wrapped edges of the sheet meet. The seam typically extends the length of the sheet in a position that is substantially parallel with the longitudinal axis of the insert or the bat frame. Multilayered composite inserts utilize two or more sheets, each having a separate seam. Often the longitudinally extending seams of two or more sheets will generally overlap each other. These longitudinally extending seams can be subjected to large impact loads, particularly when the seam or seams align with the line of action of contact between the ball and the bat, commonly referred to as the xe2x80x9cline of actionxe2x80x9d of the bat. The line of action of the bat also refers to the longitudinal portion of the bat, which upon impact with a ball, receives an impact load and transmits the load longitudinally to the handle of the bat. It is not uncommon for bats having a composite layer and a longitudinally extending seam to crack, separate, or otherwise fail at a point along the seam. Further, a bat including at least one composite layer having a longitudinally extending seam, can have inconsistent or varied performance characteristics depending upon the orientation of the bat, and in particular the location of the seam of the composite layer, in relation to the location of impact with the ball. The slugging performance of such a bat when impacted by a ball along the composite layer""s longitudinal seam will be lower than when a ball contacts the bat at a location away from the longitudinal seam.
Thus, despite the advantages offered by composite materials, there are a number of drawbacks associated with using such materials including the potential for reduced elastic deflection, a tendency of the composite layers to separate over time due to inter-laminar shear, the susceptibility of the composite insert to fail along the longitudinal seam of the insert, and inconsistent slugging performance resulting from a longitudinal seam of a composite layer of a bat.
As a result, there is a need for a tubular bat that offers at least some of the advantages of composite materials without the constraints. There is a need for a tubular bat that provides excellent slugging performance and improved durability. There also is a need for a multi-wall bat which has a relatively thin barrel wall and yet exhibits excellent durability. Further, there is a need for a single wall bat having the excellent durability characteristic of most single wall bats as well as improved slugging performance. It would be advantageous to provide a bat including an insert having at least one composite layer with an improved seam orientation that is less susceptible to failure and therefore provides improved reliability. What is needed is a bat having an insert with at least one layer of composite material that provides the bat with consistent slugging performance.
The present invention provides an improved baseball or softball bat with superior durability characteristics and little or no reduction in bat performance. The invention does so by providing a relatively thin, light (but strong) composite material, with directional strength characteristics to resist dent-causing forces, in bonded relationship to a metal carrier. For example, the present invention includes a single- or multi-wall tubular bat having at least one composite layer, with its greatest strength in a substantially circumferential direction, bonded directly to a tubular member which deflects upon ball impact.
According to a principal aspect of the invention, a bat includes a tubular frame and a tubular insert reinforced with at least one composite layer. The composite layer has its greatest strength in a substantially circumferential direction and is bonded to at least a portion of the outer surface of the insert. The composite layer provides several advantages, including improved durability with little or no reduction in performance. Because the composite layer adds strength and stiffness to the insert in the circumferential direction, it helps prevent local plastic deformation caused by circumferential stresses while allowing the frame and insert to deflect sufficiently in the axial direction to transfer substantial energy back to the ball as it leaves the surface of the bat. In another embodiment, the composite layer(s) is bonded to at least a portion of the inner surface of the insert.
The present invention also contemplates the use of multiple composite layers of varying lengths and different strength characteristics bonded to the impact portion and/or the insert of a bat so that a manufacturer can add strength and stiffness to a bat where it is needed and in the direction that it is needed. Because the intended use of a bat often drives its design, the various attributes of the composite layers, such as length, thickness, location on a bat, or orientation of fibers, may be selected to suit a particular application.
Another embodiment, which exhibits excellent durability and performance characteristics for hitting a softball, has two composite layers bonded to the outer surface of a tubular sleeve. A longer, first composite layer having its fibers oriented substantially at 0 degrees relative to the axis of the bat is applied directly to the outer surface of the sleeve. A shorter, second composite layer having its fibers oriented substantially at 90 degrees relative to the axis of the bat is placed on top of the first layer, with the second layer being positioned closer to the xe2x80x9csweet spot.xe2x80x9d
According to another preferred aspect of the invention an insert for a bat includes a substantially tubular body and at least one sheet. The tubular body extends along a longitudinal axis. The body has internal and external surfaces. The sheet has a proximal edge, a distal edge, and first and second side edges. The sheet is coupled to at least a portion of one of the internal and external surfaces of the body such that the first and second edges each extend from the proximal edge to the distal edge along a path that is substantially non-parallel with the longitudinal axis.
According to another preferred aspect of the invention a ball bat includes a substantially tubular frame, a substantially tubular body and at least one sheet. The frame extends along a longitudinal axis. The frame has a handle portion and a primary hitting portion. The body is coaxially aligned with the hitting portion of the frame. The sheet has a proximal edge, a distal edge, and first and second side edges. The sheet is coupled to at least a portion of one of the hitting portion of the frame and the body such that the first and second edges each extend from the proximal edge to the distal edge along a path that is substantially non-parallel with the longitudinal axis.
According to another preferred aspect of the invention a substantially tubular insert for a bat extends along a longitudinal axis. The insert includes a plurality of layers. Each layer forms at least part of a tubular shape and connects to at least one of the other layers. Each layer has a proximal edge, a distal edge, and first and second side edges. The first and second edges of each layer extend from the proximal edge to the distal edge along a path that is substantially non-parallel with the longitudinal axis.
According to another preferred aspect of the invention, a method of manufacturing a composite insert for a ball bat includes the steps of obtaining an elongate, generally cylindrical mandrel having a periphery and extending along a longitudinal axis, and forming at least first and second layers of composite material into a predetermined shape. Each layer has a proximal edge, a distal edge, and first and second side edges. The method also includes wrapping the first layer about at least a portion of the periphery of the mandrel such that the first and second edges of the first layer each extend from the proximal edge to the distal edge along a path that is substantially non-parallel with the longitudinal axis, and wrapping the second layer about at least a portion of the first layer such that the first and second edges of the second layer each extend from the proximal edge to the distal edge along a path that is substantially non-parallel with the longitudinal axis. The method further includes removing the mandrel from the at least first and second layers.